In the manufacture of soft tissue products such as facial, bath and towel tissue, an aqueous suspension of papermaking fibers is deposited onto a forming fabric from a headbox. The newly-formed web is thereafter dewatered, dried and creped to form a soft tissue sheet. The trend in premium tissue manufacture has been to provide softer, bulkier, less stiff sheets by layering, throughdrying and basis weight reductions. Layering, which requires a headbox equipped with headbox dividers, enables the tissue manufacturer to engineer the tissue by placing softer feeling fibers in the outer layers while placing the stronger fibers, which generally do not feel as soft, in the middle of the tissue sheet. Throughdrying enables the manufacturer to produce a bulky sheet by drying the sheet with air in a noncompressive state. Reducing the basis weight of the sheet reduces its stiffness and, when used in conjunction with throughdrying, a single-ply tissue sheet of adequate caliper and performance for a premium product can be attained.
However, producing a premium tissue product of adequate softness, bulk and strength on conventional (wet-pressed) tissue machines is not easily accomplished. For example, layering requires the purchase of a layered headbox, which is expensive. Higher bulk can be achieved by embossing, but embossing normally requires a relatively stiff sheet in order for the sheet to retain the embossing pattern. Increasing sheet stiffness negatively impacts softness. Conventional embossing also substantially reduces the strength of the sheet and may lower the strength below acceptable levels in an effort to attain suitable bulk. Reducing the basis weight of the sheet will decrease its stiffness, but may require that two or more of such low basis weight sheets be plied together to retain the desired caliper and performance. In terms of manufacturing economy, multiple-ply products are more expensive to produce than single-ply products, but single-ply products generally lack sufficient softness and bulk, especially when manufactured on conventional machines.
Accordingly there is a need for a simple means of enabling conventional tissue machines to produce premium quality tissue sheets having adequate softness, bulk and strength without the expense of purchasing a layered headbox or a throughdryer, or manufacturing multiple plies.